Inspection apparatus and method using particle beam and the particle-beam-applied apparatus

ABSTRACT

The inspection apparatus uses a particle beam and has a high throughput by obtaining a characteristic frequency corresponding to the characteristic quantity of focusing-shift from a Fourier spectrum of a sample image using a focusing-shift evaluator. A beam blur profile is produced corresponding to the characteristic frequency in a beam blur profile generator. A component of the beam-blur profile is removed from the sample image stored in one dimensional image memory using a de-convolution operator. A dimensional measurement is performed in a critical dimension evaluator for an obtained sample image. Since time spent for focus adjustment using particle beam scanning is obviated, it is possible to reduce the inspection time for a dimension and an appearance abnormality of a semiconductor element.

This is a continuation application of U.S. Ser. No. 09/116,345, filedJul. 16, 1998 now U.S. Pat. No. 6,140,644.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a scanning microscope using a particlebeam. More specifically, the present invention relates to an optimuminspection apparatus using a particle beam for performing observation orinspection of a fine dimension and/or an appearance structure of asemiconductor device.

2. Description of the Related Art

A known critical dimension evaluation apparatus using an electron beamas a particle beam acquiring a sample image based on secondary electronsby scanning an electron beam on a semiconductor sample and inspecting adimension concerning the characteristic pattern for the sample isdisclosed in Japanese Patent Application Number 60-161514. A knownappearance inspection electron beam apparatus inspecting an abnormalityof a sample by comparing an image of a scanning electron microscope witha standard pattern is disclosed in Japanese Patent Application Number5-258703. A method introduced by these apparatus has high resolution forthe image compared to an inspection method using an optical source andis very useful for inspecting a sub-micron semiconductor pattern.

In the prior art apparatus, an optimum focus adjustment of an electronlens system is performed based upon signals from at least 3 sampleimages obtained by scanning the electron beam on the same sample underdifferent conditions of focusing shift of the electron lens system. Inorder to reduce the time spent for focus adjustment, a focus adjustmentmeans for detecting a height of a sample using a height sensor usinglight reflection (Z sensor) and adjusting the focus of an electron lenssystem based upon a table produced in advance to reduce the deviation ofa height of a sample from the standard is indicated in a Japanese patentapplication number 8-273575. Since there are such problems that a samplesurface measured by the Z sensor does not completely accord with anextreme surface of the sample and that has a disadvantage in areappearance of the focus adjustment due to hysteresis of magnetizationin the electron lens system, resolution of the sample image decreasedwithout the focus adjustment using an electron beam scanning.

A method for obtaining a high resolution for a sample image based uponmathematical conversion (integral conversion) of the sample image usinga beam profile measured in advance is introduced in a Japanese patentapplication number 2-181639. However, this method does not considervariation of the beam profile due to variation of the focusing-shift foreach spot from which the sample image is taken.

SUMMARY OF THE INVENTION

It is necessary for the above inspection apparatus to improve itsthroughput since a quantity for an inspection is increased by animproved resolution. However, in the prior art, time spent in adjustinga focus of the beam accompanied with the beam scanning resulting in anextreme deterioration of an inspection throughput was not taken intoconsideration. There is still a considerable problem that although it isnecessary to execute pluralities of electron beam irradiation on asample for performing a focus compensation, the irradiation causescontamination on the sample which varies the width of wiring circuit inthe sample. Further, there is a problem that because excessiveirradiation of the electron beam causes the sample to be electrified,the electron beam used to irradiate the sample is affected so that anacquired sample image causes distortion which deteriorates the accuracyof critical dimensional measurement.

An object of the present invention is to provide an inspection apparatususing a particle beam having high resolution and high throughput.

The above-mentioned object of the invention is achieved by performing ablur-separated image calculation in the inspection apparatus having asample-image-obtaining means which scans the particle beam on a sampleand a sample inspection means which uses the numerical operation of asample image for an inspection. The inspection apparatus has afocusing-shift-detection means which derives the characteristic quantityof a focusing-shift from the sample image, a beam-blur-profilegeneration means which generates a beam-blur profile, corresponding to ablur of the particle beam, based upon the characteristic quantity of thefocusing-shift and a blur-separation means which generates ablur-separated image based upon a separation or a reduction of acomponent of the beam-blur profile in the sample image.

The focusing-shift-detection means according to the present inventiondetects a certain spatial frequency of a Fourier spectrum of the sampleimage as the characteristic quantity of the focusing-shift.

Furthermore, there is provided means for memorizing by correlating thesample image, the beam-blur profile and the blur-separated image andmeans for displaying simultaneously a set of the sample image, thebeam-blur profile and the blur-separated image.

The invention also encompasses an inspection method using the inspectionapparatus. The method involves moving a sample to an inspection pointfor the sample after an adjustment of an astigmatism for the particlebeam is completed, acquiring at most two different kinds of sampleimages by scanning the particle beam for each inspection point of thesample and inspecting the sample based upon the sample images.

The inspection apparatus of the present invention also includes meansfor producing a first display image acquired by scanning the particlebeam on the sample, means for deriving the characteristic quantity ofthe focusing-shift based upon the first display image, means forproducing a second display image based upon the characteristic quantityof the focusing-shift and the first display image and means forinspecting the sample based upon the second display image.

These and other objects, features and advantages of the presentinvention will become more apparent in view of the following detaileddescription of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an electron beam critical dimensionevaluator according to an embodiment of the present invention;

FIG. 2 is an example display;

FIG. 3 is a flow chart of a dimension measurement process;

FIG. 4 is a flow chart for generating a blur-separated image;

FIG. 5 is a graph showing an example Fourier spectrum of a sample image;

FIGS. 6(a)-6(f) are graphs showing a sample image in several kinds offocusing-shifts and their corresponding Fourier spectrum;

FIG. 7 is a flow chart of a de-convolution operation;

FIG. 8 is a block diagram showing an appearance inspection electron beamapparatus according to an embodiment of the present invention;

FIG. 9 is a flow chart of an appearance inspection;

FIG. 10 is a block diagram showing a signal flow in the electron beamcritical dimension evaluator according to one embodiment of the presentinvention; and

FIG. 11 is a block diagram showing another signal flow in the electronbeam critical dimension evaluator according to another embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In a scanning electron beam microscope, a sample image i is shown by aconvolution of S and b as indicated in equation (1) on the conditionthat a secondary particle radiation coefficient distribution is S and anintensity distribution of a particle beam at an optimum focus is b.

i(x, y)=S(x, y){circle around (×)}b(x, y)  (1)

where (x, y) represents a two dimensional coordinate system. Aconvolution operation is defined by an integral conversion as indicatedin equation (2). $\begin{matrix}\begin{matrix}{{{S\left( {x,y} \right)} \otimes {b\left( {x,y} \right)}} = \quad {\int{{x}{Y}\quad {S\left( {{x + X},{y + Y}} \right)}{b\left( {X,Y} \right)}}}} \\{= \quad {\int{{x}{Y}\quad {S\left( {X,Y} \right)}{b\left( {{X - x},{Y - y}} \right)}}}}\end{matrix} & (2)\end{matrix}$

An obtained sample image I is represented by a convolution of S and B asindicated in equation (3) on the condition that an intensitydistribution of the particle beam is B in case that no focus adjustmentis done.

I(x, y)=S(x, y){circle around (×)}B(x, y)  (3)

where a particle beam B has a blurring of a certain amount from theparticle beam b.

If a beam-blur profile showing the blurring is D, B is shown by aconvolution of b and D as indicated in equation (4).

B(x, y)=b(x, y){circle around (×)}D(x, y)  (4)

Since an associative law can be used in a convolution operation,equation (5) is realized based upon equations (1), (3) and (4).

 I(x, y)=i(x, y){circle around (×)}D(x, y)  (5)

If the beam-blur profile D is obtained, according to equation (5) thesample image i can be obtained at an optimum focus having a blurringremoved by a reverse operation of convolution (i.e., a de-convolutionoperation). It should be understood that a much higher resolution of animage can be obtained if an amount close to B instead of D is used.

If a table showing a relation between a frequency spectrum appearance ofsample images having several kinds of focusing-shifts and the beam-blurprofile D is obtained in advance, a beam-blur profile regarding anarbitrary sample image can be produced. Further, the beam-blur profile Dcan be calculated by obtaining in advance several kinds of images havinga focusing-shift regarding a standard sample and by comparing thoseimages with an image at an optimum focus (perform a de-convolutionoperation using equation (5)).

Accordingly, the present invention obviates a focus adjustment timebased upon a particle beam scanning and reduces an inspection time sincea focusing-shift for the sample image of a particle beam scanningmicroscope based upon the introduced means can be removed. Moreover, atime for processing these operations can be reduced to a time foracquiring the sample image by using a parallel processed computer.

FIG. 1 is a block diagram showing an electron beam critical dimensionevaluator based upon a first embodiment of the present invention. A mainbody 1 includes a FE electron source 2, a variable limiting aperture 4,electron lenses 5, 5′, a deflection plate 7, a sample stage 9 movablyholding a sample 6 and a secondary particle detector 8. The main body 1also includes a laser 10, lens system 11, 11′ and a laser positiondetector 13 for detecting a height of the sample 6. A vacuum chamberholding the above-mentioned devices and a pumping system are omitted.The secondary particle detector 8 has a fluorescence plate and aphoto-multiplier, and detects secondary electrons. The main body 1 isconnected to a main controller 30 via a deflection controller 20 and asecondary particle signal control system 21. A control system for theelectron source 2, the variable aperture 4, the electron lens 5, andsample stage 7 is omitted. The laser position detector 13 and theelectron lens 5′ are connected to a focusing-lens controller 14. Adisplay 31, a sample memory 32, a sample inspection block including ameasuring position finder 70, one dimensional image memory 71 and acritical dimension evaluator 72 are connected to the main controller 30.

An operation of the main body 1 will now be described. The beam size ofan electron beam 3 emitted from the electron source 2 is regulated atthe variable limiting aperture 4, focused at the electron lenses 5, 5′and irradiated on the sample 6. The electron beam 3′ is decelerated atthe electron lens 5′. An acceleration voltage of the electron beam 3′ onthe sample is 800V. A beam diameter of the electron beam 3′ is 5 nm andits current is 10 nA. If the electron beam 3′ is irradiated on thesample 6, secondary electrons or reflection electrons corresponding tomaterial and structure of the sample are generated from the part beingirradiated. The secondary particle detector 8 detects the secondaryelectrons and converts to detected result into an electrical signal (asecondary electron signal). The deflectors 7 deflect the electron beam3′ and cause it to scan on the sample 6 based upon a scanning deflectionsignal generated from the scanning circuit in the deflection controller20. The main controller 30 stores the secondary electron signal, withthe scanning deflection signal used for addressing in a buffer memory ina secondary particle detector 21, into the sample memory 32.Simultaneously, the main controller 30 sends the secondary electronsignal to the display 31 to display a SEM image (a scanning electronmicroscope image) of the sample having the secondary electron signal asa luminance signal. The main controller 30 still sends the sample imageto the sample inspection block and performs dimensional measurementselectively at a spot being set in advance. In the sample inspectionblock, the measuring position finder 70 having a pattern of measuringspot in advance checks the sample image stored in the sample memory 32,instructs the main controller 30 where a required spot to measure is,has the main controller 30 derive an enlarged sample image again,generates a one dimensional image required to measure from latter imageand has it stored into the one dimensional image memory 71. The criticaldimension evaluator 72 abstracts a characteristic position from the onedimensional image stored in the one dimensional image memory 71 andcalculates its dimension. The main controller 30 stores thesecalculation results into a memory device (not shown) and displays theresults onto the display 31, if required. The variation of a height ofthe sample 6 is detected based upon the change of the position at whicha reflection light 12′ of a light 12 emitted from the laser 10 isincident to the laser position detector 13. The focusing lens controller14 regulates an intensity of the electron lens 5′ based upon a signalfrom the laser position detector 13 and always controls the electronbeam 3′ to focus on the sample 6. However, this method includes aninconsistent error because an optically detectable sample surface andone that is detectable by an electron beam do not match completely.Accordingly, an optimum intensity of the electron lens 5′ is derived byscanning an electron beam, by obtaining several pieces of sample imageshaving a different intensity of the electron lens 5′ and by comparingthose sample images with each other.

A feature of this embodiment is to (1) detect the characteristicquantity of focusing-shift from the sample image, (2) produce thebeam-blur profile corresponding to the focusing-shift and (3) remove aninfluence of the beam-blur profile from the sample image. Specifically,as shown in FIG. 1, a feature is to have an image-blur-separation blockconnected to the main controller 30. The focusing-shift evaluator 60reads the sample image obtained by scanning the electron beam 3′ on thesample 6 from the sample memory 32, detects the characteristic quantityof focusing-shift based upon the appearance of Fourier spectrum for thisimage and sends the characteristic quantity of focusing-shift to abeam-blur-profile generator 61. The beam-blur-profile generator 61generates a beam-blur profile from a data table held in advance for thebeam blur profile corresponding to the characteristic quantity offocusing-shift through data interpolation and stores the beam-blurprofile in a beam-blur-profile memory 50. A de-convolution operator 51generates a one dimensional image of the sample at an optimum focus byperforming a de-convolution operation separating a component of thebeam-blur profile from the one dimensional image and stores the onedimensional image in a blur-separated image memory 52. In the prior art,the one dimensional image cut out from the sample image stored in thesample memory 32 is used in the sample inspection block for measuring afine dimension on the sample. However, in the embodiment of the presentinvention, a measurement of the fine dimension is performed by removingthe influence of focusing-shift and by using the one dimensional imagestored in the blur-separated image memory 52. By performing this finedimensional measurement, it is unnecessary to scan the electron beamexcessively on the sample to search for the optimum focus.

FIG. 2 is a diagram showing an example display in which a flow for aseries of the above de-convolution operations is clearly understood. Abeam-blur profile 150 is generated from a sample image 132 having aslight focusing-shift. A blur-separated image 152 is generated byremoving a component of the beam-blur profile 150 from the onedimensional image 170 cut out from the sample image 132 using thede-convolution operation. Then, a fine dimension (that is, a diameter ofa hole) of the sample is measured by using a characteristic position ofthe blur-separated image 152. For the purpose of an operator'sconfirmation, data as shown in FIG. 2 can be put together and storedinto a memory unit (not shown).

FIG. 10 is a block diagram showing a signal flow in a process as in FIG.2. A de-convolution operation is processed for a one dimensional imageabstracted from the sample image to reduce calculation time. A methodshown in FIG. 11 is appropriate to perform more accurate processingalthough the calculation time increases. In other words, thede-convolution operation is performed for the sample image having a twodimensional image, a measurement position is abstracted for the sampleimage, a one dimensional image is produced and a critical dimensionevaluation is performed.

FIG. 3 is a flow chart showing the steps of measurement. A feature ofFIG. 3 is to perform a focus adjustment and an adjustment of theastigmatism for an electron beam using a standard sample being set onthe sample stage. Another feature is that dimensional measurement cannot be performed unless this adjustment is completed. The latter featureis a remedy to deterioration of accuracy for the blur-separated imageproduced by the de-convolution operation since the beam-blur profile isnot produced normally if the adjustment of the astigmatism is notperformed. An electron beam critical dimension evaluator introduced inan embodiment of the present invention is programmed to end abnormallyand to display an abnormality to an operator in case that the abovefocus adjustment and the adjustment of the astigmatism result in failureduring a normal automatic measurement. If the adjustment is completednormally, the sample is moved to put an arbitrary position of the sampleregistered in advance just below the electron beam. Detection of aheight of the sample using the Z sensor and focus adjustment of theelectron lens are performed simultaneously with this sample movement.Then a sample image is derived by scanning the electron beam on thesample, the image is stored, a one dimensional image required fordimensional measurement is cut out and the one dimensional image isstored thereafter. For deriving the sample image, deriving an enlargedsample image again for adjusting to a necessary scale factor oftenoccurs. Accordingly, in a procedure for the following dimensionalmeasurement, the number of sample images obtained by the electron beamscanning is one or two (ie. at most two). Then a blur-separated image isproduced from a stored sample image and one dimensional image, and adimensional measurement for this blur-separated image is performed. Ifthe above procedure is ended, the same procedure is repeated aftermoving to the next sample position. Further, in FIG. 3, although anacquisition of the sample image and a measurement of dimension areperformed simultaneously, it is possible to perform them separately.

In the prior art, it took 10 seconds to complete a critical dimensionevaluation at a spot of a sample. The contents of the evaluationincludes: 2 seconds for a focus adjustment by moving the sample andusing the Z sensor; 5 seconds for the focus adjustment by scanning abeam; 2 seconds for deriving a sample image and detecting acharacteristic position; and 1 second for producing and inspecting theone dimensional image. In the embodiment of the present invention, ittakes 6 seconds to finish measurement as a whole so that a second forproducing a blur-separated image is added while the focus adjustment bya beam scanning is unnecessary. It is possible for the blur-separatedimage to reduce its production time according to a parallelcomputerization.

FIG. 4 is a flow chart showing the generation of a blur-separated imageas in FIG. 3. A detailed description is given for detecting thecharacteristic quantity of focusing-shift, i.e., the content offocusing-shift evaluator 60 as in FIG. 1. The sample images read fromthe sample memory are all integrated in one dimensional direction. ThenFourier transform is applied to a signal resulting from the integration.In this case, an intensity of the Fourier transformed result isstandardized as a total signal amount. An image applied Fouriertransform (that is, a Fourier spectrum) is shown in FIG. 5. An optimalintensity close to a noise level is set. LINE 1 in FIG. 5 shows theoptimal intensity. An asymptotic line for a variation part of theFourier spectrum is shown as LINE 2. A spatial frequency F0 calculatedbased upon an intersection of LINE 1 and LINE 2 is detected as thecharacteristic quantity of focusing-shift. Although a focusing-shiftevaluation is performed for the sample image, the same evaluation may bedone for the one dimensional image. In such case, since S/N (signal tonoise ratio) of a signal gets worse slightly, the accuracy ofcalculation also decreases. However, calculation time can be reduced.

FIGS. 6(a)-6(f) are graphs showing a sample image in case of settingseveral kinds of focusing-shifts regarding a standard sampleintentionally and an example of a Fourier spectrum. FIGS. 6(a) and 6(b)correspond to a sample image with a great shift of focusing. FIGS. 6(c)and 6(d) correspond to a sample image with a small shift of focusing.FIGS. 6(e) and 6(f) correspond to a sample image with optimum focus. Thesample image is already integrated one-dimensionally and an intensity isstandardized. The characteristic quantity of focusing-shift as in FIGS.6(a)-6(f) is on a level that a Z sensor can not compensate and is a verysmall amount. Since a spatial frequency F0 varies with respect to thefocusing-shift, it is understandable to convert the frequency F0 to thecharacteristic quantity of focusing-shift and to read it. Further, it ispossible to obtain a beam-blur profile based upon a de-convolutionoperation of the sample image at the optimal focus from the sample imageat an arbitrary focus and to generate a table showing the relationshipbetween the spatial frequency F0 and the beam-blur profile (it isnecessary to increase S/N of the sample image and to widen a dynamicrange for obtaining the beam-blur profile as accurately as possible).The beam-blur profile generator 61 in FIG. 1 holds this table andproduces a beam-blur profile based upon a compensation of the data tablefor an arbitrary spatial frequency. Here, a height of LINE 1 and a slopeof LINE 2 are respectively, determined by the characteristics ofbeam-blur function, common for an electron beam critical dimensionevaluator of the same electron optical system design (that isproduct-type). However, they are slightly varied for each apparatus ofthe same product-type. Because of this feature, in the electron beamcritical dimension evaluator introducing an embodiment of the presentinvention, data held in the focusing-shift evaluator 60 and thebeam-blur-profile generator 61 is divided into a common specificationportion and a compensation portion and a data of the compensationportion is restored for each apparatus. A standard sample is set on asample stage for performing such correction operation. A programperforming correction operation automatically using this standard sampleis installed in the main controller 30. Although a focusing-shift beamblur profile is produced based upon the table, it is possible to producethe beam blur profile using an appropriate approximation function. Whenusing such approximation function, computing time can be reduced.

A description concerning a de-convolution operation performed in thede-convolution operator 51 in FIG. 1 will now be described. In theembodiment of the present invention, a feature is that a method using aconvolution operation and a repetitive comparison is employed instead ofa simple de-convolution operation. Such a method has a tolerance tonoise. FIG. 7 is a flow chart showing a de-convolution operation. Anoperation of this flow chart includes: (1) assuming an appropriateblur-separated image (first blur-separated image) initially; (2)obtaining a result for a convolution operation of the firstblur-separated image and a beam-blur profile; (3) obtaining a differenceimage for them by comparing the result with an actual sample image; and(4) compensating the first blur-separated image to decrease an intensityof the difference image and returning to a step (2). The above operationis a repetitive process. Further, the above operation converges throughrepetitive process of more than 10 times and the operation time isapproximately 100 ms using a special purpose circuit havingsum-of-products operation paralleled.

Since a focus adjustment based upon an electron beam scanning can beobviated by employing the embodiment of the present invention, there isan effectiveness to be able to reduce damage for a sample such as asemiconductor element due to electron beam irradiation and dimensionalmeasurement time can be reduced.

FIG. 8 is a block diagram showing an appearance inspection electron beamapparatus based upon a second embodiment of the present invention. Aconfiguration as a whole is as well as the electron beam criticaldimension evaluator shown in FIG. 1. An internal configuration of asample inspection block connected with a main controller 30 and aconfiguration of a program built in the main controller 30 are differentfrom those in FIG. 1. Although detailed design of an electron opticalsystem and a secondary particle detector are different as well, adescription of the difference is omitted since the difference is lessimportant. A beam diameter of an electron beam 3′ is 100 nm and itscurrent is 100 nA. The sample inspection block includes a standard-imagememory 40, an image-difference operator 41 and a difference-image memory42. The main controller 30 reads a sample image obtained by scanning theelectron beam 3′ on a sample 6 from a sample memory 32, sends the sampleimage to the sample inspection block and detects a sample abnormalitysuch as foreign matters by comparing the sample image with a standardimage. In the sample inspection block, the sample image stored in thesample memory 32 and a standard display image stored in advance in thestandard image memory 40 are compared by the image-difference operator41 and the comparison result is stored in the difference-image memory42. If the difference image satisfies an arbitrary standard, the imageis stored as an abnormality in a memory unit (not shown) and isdisplayed in the display 31.

A feature of this embodiment is to (1) detect the characteristicquantity of focusing-shift from the sample image, (2) produce abeam-blur profile corresponding to the focusing-shift and (3) remove aninfluence of the beam-blur profile from the sample image. Specifically,as shown in FIG. 8, a feature is to have an image-blur-separation blockconnected to the main controller 30. A focusing-shift evaluator 60 readsa sample image from the sample memory 32, detects the characteristicquantity of focusing-shift based upon an appearance of a Fourierspectrum of this sample image and sends the characteristic quantity to abeam-blur-profile generator 61. The beam-blur-profile generator 61generates a beam-blur profile from the data table held in advance forthe beam blur profile corresponding to the characteristic quantity offocusing-shift through data interpolation and stores the beam-blurprofile into a beam-blur-profile memory 50. A de-convolution operator 51generates a sample image at an optimum focus by performing ade-convolution operation separating a component of the beam-blur profilefrom the sample image and stores the sample image to a blur-separatedimage memory 52. An appearance inspection of the sample is performed bycomparing the sample image stored in the blur-separated image memory 52,having an influence of the focusing-shift removed, with a standard imagestored in the standard image memory 40. Based upon this inspection, itis unnecessary to scan an electron beam on the sample excessively andthe inspection can be performed by using the sample image at an optimumfocus.

FIG. 9 is a flow chart showing a performance of an appearanceinspection. Just as with the embodiment shown in FIG. 1, an appearanceinspection electron beam apparatus is set not to be able to perform anappearance inspection unless a focus adjustment and an adjustment of theastigmatism is completed. If the above adjustment is normally done, thesample is moved to put an arbitrary position of the sample registered inadvance just below the electron beam. Detection of a height of thesample using a Z sensor and a focus adjustment of an electron lens areperformed simultaneous with this sample movement. Then the sample imageis derived by scanning the electron beam on the sample and the image isstored. A blur-separated image is produced from the stored sample image.An appearance inspection of the sample is performed for thisblur-separated image and foreign matters on the sample are detected. Ifa series of steps according to the above procedure is ended, the sameprocedure is repeated after moving to the next sample position. Further,in FIG. 9, although an acquisition of the sample image and itsappearance inspection are performed simultaneously, it is possible toperform them separately.

In the prior art, it took 100 ms to perform an appearance inspection fora spot of the sample. This time is almost equal to an acquisition timeof a sample image since the sample image is derived while moving asample stage. Although a resolution of the sample image at an optimumfocus obtained by scanning an electron beam several times on the sampleis 100 nm, an average resolution of the sample image in case of a focusadjustment using a Z sensor is 200 nm. In the embodiment of the presentinvention, since a sample image at an effectively optimum focus isderived and an appearance inspection for that focus is performed,resolution of the inspection is improved many times as much. The timespent for an operation in the image blur-separation block as in FIG. 9is 100 ms using a special purpose circuit having sum-of-productsoperation paralleled. However, since the special purpose circuit portionis arranged by two channels being paralleled and multiplied, aninfluence to an actual inspection time is completely removed.

Through embodiments of the present invention, an appearance inspectionusing a sample image at an effectively optimum focus is performed,thereby improving resolution of an inspection.

According to the present invention, since the time spent for focusadjustment based upon the particle beam scanning is obviated, it ispossible to reduce an inspection time for a dimension and an appearanceabnormality of a semiconductor element. Further, there is provided animproved accuracy of the inspection since contamination and/orelectrification of the sample based upon an excessive irradiation of theelectron beam can be reduced. Additionally, a defection analysis of asemiconductor integrated circuit is performed during a short period oftime. Hence, there is another advantage to improve its yield rate in anearly stage.

While the present invention has been described above in conjunction withthe preferred embodiments, one of ordinary skill in the art would beenabled by this disclosure to make various modifications to theseembodiments and still be within the scope and spirit of the presentinvention as defined in the appended claims.

What is claimed is:
 1. A method of measuring a fine dimension of anobject sample comprising the steps of: generating a charged particlebeam; irradiating said charged particle beam to an object sample;detecting secondary charged particles radiated from said object sample;generating a plurality of first values of characteristic quantity offocusing shift from a plurality of Fourier spectrum of chargedparticle-beam profiles of a standard sample respectively obtained atdifferent focus shift quantities and a second value of characteristicquantity of focusing shift from a Fourier spectrum of a chargedparticle-beam profile of said object sample; storing said chargedparticle-beam profiles of standard sample respectively corresponding tosaid first values of characteristic quantity, and said first values ofcharacteristic quantity of focus shift of said standard sample and asecond value of characteristic quantity of focus shift of said objectsample; estimating a beam-blur profile of said standard sample whichcorresponds to said second value of characteristic quantity from chargedparticle-beam profiles stored in said memory; and generating ablur-separated image based upon a reduction of said chargedparticle-beam from said object sample image using a de-convolutionoperations.
 2. The method according to claim 1, wherein said chargedparticle beam generated in said step of generating a chargedparticle-beam is an electron beam.
 3. An inspection apparatus employinga particle-beam having a sample-image-obtaining means for scanning saidparticle-beam on an object sample, the apparatus comprising: afocusing-shift-evaluator which generates a plurality of first values ofcharacteristic quantity of focusing shift from a plurality of Fourierspectrum of particle-beam profiles of a standard sample respectivelyobtained at different focus shift quantities, and a second value ofcharacteristic quantity of focusing shift from a Fourier spectrum of aparticle-beam profile of said object sample; a memory for storing saidparticle-beam profiles of said standard sample respectivelycorresponding to said first values of characteristic quantity and saidfirst values of characteristic quantities of focus shift of saidstandard sample and said second value of characteristic quantity offocus shift of said object sample; a beam-blur-profile generator whichestimates a beam-blur profile of said standard sample which correspondsto said second value of characteristic quantity from particle-beamprofiles stored in said memory; and blur-separation means whichgenerates a blur-separated image based upon a reduction of saidparticle-beam from said object sample image using a de-convolutionoperation.
 4. The inspection apparatus according to claim 3, whereinsaid first values of characteristic quantity are respective spatialfrequencies required from each Fourier-spectrum of said particle-beamprofiles.
 5. The inspection apparatus according to claim 3, furthercomprising: a display unit for displaying a set of said object sampleimage, said particle-beam profile of said object sample and saidblur-separated image of said object sample.
 6. An inspection methodusing a particle beam comprising the steps of: performing an adjustmentof an astigmatism for said particle beam; moving an object sample to oneof a plurality of inspection points set in advance for said objectsample; evaluating a plurality of first values of characteristicquantity of focusing shift from a plurality of Fourier spectrum ofparticle-beam profiles of a standard sample respectively obtained atdifferent focus shift quantities and a second value of characteristicquantity of focusing shift from a Fourier spectrum of a particle-beamprofile of said object sample; storing said particle-beam profiles ofsaid standard sample respectively corresponding to said second value ofcharacteristic quantity, and said first values of characteristicquantity of focus shift of standard sample and second value ofcharacteristic quantity of focus shift of said object sample; estimatingbeam-blur profiles of said standard sample which correspond to saidsecond value of characteristic quantity from said particle-beam profilesstored in said first memory; and separating a blur-separated image basedupon a reduction of said second focus shift of said object sample usinga de-convolution operation.
 7. The method according to claim 6, whereinthe step of moving the object sample includes a step of detecting aheight of the object sample using a Z sensor while the object sample isbeing moved.
 8. The method according to claim 7, wherein the step ofmoving the object sample also includes a step of performing focusadjustment of the electron lens while the object sample is being moved.9. The method according to claim 6, wherein the beam blur profilesestimated in said step of estimating said beam blur profiles are onedimensional images.
 10. The method according to claim 6, wherein thestep of estimating beam blur profiles corresponding to said second valueof characteristic quantity estimates by interpolating from saidplurality of particle beam profiles of said standard sample.
 11. Themethod according to claim 8, wherein the step of inspecting said objectsample includes the steps of: producing a blur-separated image from astored sample image and a one dimensional image; and performing adimensional measurement for the blur-separated image.